Source Protection Science

The Assessment Report

An Assessment Report is the technical document that contains the scientific information that the source protection plan and its policies are based on and includes:

  • Description of the local watershed and available water supplies;
  • Identification of vulnerable areas  around well supplies where drinking water sources are most sensitive to contamination and depletion;
  • Identification of the number and types of drinking water threat activities occurring  around municipal drinking water supplies; and
  • Calculation of a water budget to assess local demand versus available supply.

The scientific foundation for the source protection program in the Town of Orangeville is provided in the Assessment Report for the Credit Valley Source Protection Area.  This document can be found online at:


Tier 3 Water Budget 

Source Water Protection is about protecting drinking water quantity as well as quality. Much like a bank account, if more water is being withdrawn than is replenished, the supply will be depleted. When demand exceeds the supply, our drinking water sources can experience stress. It is important to protect water quantity in order to ensure we have enough water for all uses now and in the future.

To determine where water supplies might come under water quantity stress, the CTC Source Protection Committee completed scientific studies called Water Budgets as part of the Assessment Report. A water budget is a calculation of how much water enters and leaves a system through natural processes and human consumption. Knowing the water budget for a system allows researchers to determine if more water is being used than is available. If we understand where water quantity stresses can occur, we can take proactive measures to protect these vulnerable water supplies and prevent shortages.

Graphic courtesy of Conservation Ontario


Water budgets were conducted using a tiered approach for every watershed in the CTC source protection region. For each successive tier, the scope of the study became more focused and more complex analysis techniques were used. A Tier 3 Water Budget- the most detailed and comprehensive level of water budget analysis- was performed for the well system serving the Town of Orangeville.

The Orangeville Tier 3 Water Budget compared the available groundwater and surface water supply to existing and projected demand scenarios from all water users. Where the ratio of water demand to supply was found to be high, the system was deemed to be under water quantity stress.  

Orangeville’s water supply was identified as “stressed” under a future build-out scenario of increased water demand and drought conditions.  This indicates that Orangeville’s water system does not have any problems meeting current water demands, but there is a need to protect drinking water resources to ensure water needs can be met sustainably under future development scenarios.   

To protect drinking water supplies, areas of vulnerability called Wellhead Protection Areas for Quantity (WHPA-Q1/Q2) were defined around the Town’s wells. The WHPA-Q1/Q2 is the area where groundwater use and changes in the ability for groundwater to recharge the aquifer could affect the quantity of water available at Town wells.  

In the WHPA-Q1/Q2, significant drinking water quantity threats include:

  • Activities that take water from an aquifer, but do not return water to that same aquifer.  (e.g. domestic wells, or industrial water takings for agriculture or aggregate operations) 
  • Activities the decrease the recharge to an aquifer - If water cannot soak into the ground to replenish the water supply, the long term yield of the water supply is impaired. Examples of activities that impair water recharge include any conversion of land to an impervious surface (e.g. paving new parking lots, building/construction activities, and new land use developments).  

Activities identified as significant water quantity threats in the WHPA-Q1/Q2 are subject to water quantity protection policies in the CTC Source Protection Plan. Water quantity policies aim to protect the long term sustainability of local drinking water sources by calling for responsible development in water quantity protection areas.